[webkit-dev] ASYNC attribute for <script>?

Peter Kasting pkasting at google.com
Tue Apr 28 10:04:49 PDT 2009

Steve Souders, whom most of you have hopefully heard of due to his work with
YSlow etc., proposed something in one of the Chrome bug trackers that I
thought was more appropriate for WebKit in general, or perhaps HTML5 (Hixie:
CCed you so you can give feedback on where to send this).

I am pretty ignorant of all this stuff, so I'll just paste Steve's
slightly-edited proposal below for comment.



It's great that WebKit has parallel script **downloading**. But... this
still blocks page rendering of all elements below the script and still
blocks all execution of subsequent JavaScript.

I'd like an ASYNC attribute to the SCRIPT tag that implied WebKit should go
ahead and render subsequent page elements and go ahead executing subsequent
JavaScript. This would make it easy for developers deploying standalone
features (carousel, widgets, etc.) to get better page behavior.

This is esp. important for ads. It's unlikely that we can make much progress
amongst ad services to adopt performance improvements that require even a
small amount of extra JS coding. It is more likely that we could make
inroads in getting them to add a simple "async" attribute.

The key to accomplish this is that the async-loaded scripts must be able to
preserve document.write. This opens up a lot of scenarios - I certainly
haven't thought them all through. But Opera has this capability, and in my
testing it works (see
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